Die4Drive – A constant current laser diode driver with up to 2A output current.

Update 4/June/07

Moved to Rev 1.2

This adds a second POT to allow setting of threshold current.

This allows setup to give output laser power proportional to input voltage.

Also added a soft start feature.

These modifications also make the drive slightly kinder to the laser diode.

Schematic for Rev 1.2 in PDF format.

Usual rules apply – This information is provided freely for NON COMMERCIAL USE you can make one or two for your own personal use.

Drive current calculator in Excell Format for Rev 1.2

Picture of Rev1.1 and Rev1.2 side by side.

Rev 1.1 was 44mm x 20mm

Rev 1.2 is 44.5mm x 22.5mm

Rev 1.2 can still have the sense resistor fitted as 0.1 Ohm for 10x current range (up to 2A)

Driver supports CW, analogue or TTL modulation up to 200kHz.

Connection info for the driver board. Note the errata for V1.1 link resistor positions.

Up to 300mA no cooling is required. Above 300mA the PCB may be bolted to a heatsink.

To start with you will need a regulated 5V supply capable of the full diode current.

A bench PSU will do – but a fixed 5V would be a lot cheaper.

The link resistors R5, R4 & R3 set the full scale current.

By default all are shorted. This gives a full scale current of 146mA.

The Pot R1 sets the output from 0mA to full scale output.

The full scale currents are as follows:

R3	R4	R5	I Full-Scale (mA)
1	1	1	146
0	1	1	163
1	0	1	192
0	0	1	224
1	1	0	384
0	1	0	536
1	0	0	1063
Above: 1 = linked 0 = cut

The drive current may be monitored by looking at the voltage on the MON pad.

MON gives 1mV per mA, so for 100mA you would read 100mV from MON to GND.

To check the setup before connecting your diode you can short LDA to LDC.

The driver will put the current through the short and you can monitor the MON pad.

For CW operation DRV is linked to SET.

For TTL / analogue drive DRV is the input from 0 to 5V.

For the DVD recorder laser diode the lowest range is used. Here the pot is set at max.

The current is 147mA into the shorting link.

Return the pot to minimum, remove the shorting link LDA to LDC.

Connect the laser diode. (Anode A to LDA, Cathode C to LDC, N is a no-connect)

** Now is a good time to put on your laser safety goggles. **

Apply power and slowly turn up the pot.

Still reading 147mA with the pot at max.

100mW output at approx. 145mA drive.

Here is a ‘scope capture of the output current with TTL modulation.

The driver has R4 & R5 links cut to set a full scale of 1A.

(Do Not put 1A through a DVD laser diode – it WILL kill it)

Ch.1 is 5V TTL I/P, Ch.2 is 500mA/div output current.

Nice and clean & no nasty spikes.

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